LONDON , England -LRB- CNN -RRB- -- Treating flu-stricken children with anti-viral medication including Tamiflu and Relenza could do more harm than good , a new report has warned .

Researchers say not enough study has been done into the long-term effects of anti-virals on children .

Researchers from the University of Oxford found that while the anti-virals reduced the duration of illness by up to one day and a half , they had `` little or no effect '' on the likelihood of the children developing complications .

The researchers conceded that they did n't know the extent to which their report applied to the current swine flu pandemic , but said , `` based on current evidence , the effects of anti-virals on reducing the course of illness or preventing complications might be limited . ''

In compiling their report , published in the British Medical Journal , the Oxford University researchers searched the world for trials of Tamiflu and Relenza on children under 12 . They found seven in total ; four relating to flu treatment , and three to prevention .

They say none offered a big enough study to determine whether anti-virals have any effect on the chances of children developing serious flu-related complications .

`` We 've got very little data to go on . These drugs have been used on tens of thousands , in fact millions of children worldwide , and we 've found only four trials of treatments involving less than two thousand children , '' said the report 's author , Dr Matthew Thompson , a senior clinical scientist at the Department of Primary Health Care , the University of Oxford .

`` We did n't find any trials of children under one . And none of the trials was big enough to show if there 's any effect on serious complications like pneumonia or being hospitalized , '' he said .

The report found that while anti-virals reduced the duration of flu in children , they had little or no impact on the likelihood of the child developing ear infections or any other condition that may require antibiotics .

A review of one study into the effect of anti-virals on asthmatic children , who are considered to have a higher risk of developing complications from the flu virus , found that they did not reduce the risk of the asthma attacks .

The report said that one in 20 children who take Tamiflu suffer nausea and vomiting , as indicated in warnings from the drug 's manufacturer . `` That obviously can be a particular problem in young children and infants where getting dehydrated is a complication of influenza , '' Thompson said .

The three studies that focused on the use of anti-virals to prevent influenza taking hold , showed that their potential to stop the spread of flu was `` fairly small . ''

`` We 'd need to treat 13 children with the preventive course of one of these drugs to prevent one of them from getting flu , '' Thompson said .

The report 's authors suggested governments were too quick to recommend anti-virals as the first defense against the spread of swine flu . In the United Kingdom , people who suspect they have the virus are urged to phone a government helpline . If enough symptoms match the operator 's list , they 're given an online voucher so a `` flu friend '' can collect a course of Tamiflu .

`` We 're not criticizing the current Department of Health policy , but we hope they 'll inform perhaps a slight shift in policy in terms of use of these drugs , '' Thompson told CNN .

The British Department of Health said the report was right to suggest bed rest and over the counter remedies for people with mild cases of flu , but added that it was potentially dangerous to deter people with severe cases of flu from taking Tamiflu , including children .

In a statement , a spokesman said : `` Whilst there is doubt about how swine flu affects children , we believe a safety-first approach of offering anti-virals to everyone remains a sensible and responsible way forward . However , we will keep this policy under review as we learn more about the virus and its effects . ''

The British Medical Association -LRB- BMA -RRB- also adopted a cautious stance . The chairman of the BMA 's general practitioner 's committee , Dr Laurence Buckman , said doctors always have to balance the risk of major complications from swine flu with the potential side-effects of anti-virals .

`` While we know they are safe , we do know that vomiting and diarrhea can occur in some children and adults who take them , '' he said , adding `` The more we learn about these drugs the more we will know how to treat patients with the most up-to-date clinical evidence . ''

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Researchers examined studies into effects of anti-virals on children

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Found `` little or no effect '' when used on children suffering influenza

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Anti-virals were found to shorten duration of flu-like symptoms

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British Department of Health said it had `` a safety-first approach ''